1. Field of the Invention
This present invention relates to an improved method for producing steroidal sapogenins such as hecogenin from leaves of plants such as Agave sisalana. A sapogenin is a constituent of saponins; sapogenins occur naturally in the juice of certain plants in the form of the appropriate water soluble saponin. A saponin is a member of a group of glycosides, some steroidal derivatives, which are usually characterized by their property of producing a soapy lather. Chemically they consist of multiple sugar groups linked to a sapogenin nucleus by means of a glycosidic bond.
Among the sapogenins, hecogenin is of prime importance in the synthesis of corticoids. It is used as a raw material in the production of such cortical hormones as cortisone, cortisol, prednisolone, prednisone, dexamethasone, betamethasone, triamcinolone and others. Its usefulness as a synthetic starting material is due to the fact that hecogenin possesses an oxygen atom in the C-12 position which can be moved to the C-11 position. This makes it possible to introduce the 9-11 double bond which is necessary for the syntheses of the above mentioned hormones, as shown in the synthetic pathway set out in FIG. 1, described more fully hereinafter.
2. The Prior Art
As a means of obtaining crude hecogenin some prior art references disclose a fermentation process. Others describe hydrolysis at atmospheric pressure. Still others couple both of these techniques, and some even suggest the use of alcohol as a precipitating agent. Generally the use of large quantities of acid is advocated. I have found the above mentioned art unsatisfactory for the following reasons:
1. The use of large amounts of acid results in charring the plant juice; the resulting crude hecogenin is usually black and even shows the presence of calcium sulfate crystals. Also, the hecogenin yield is usually very poor.
2. The use of alcohol as a precipitating agent is very unsatisfactory since the reaction is accompanied by violent bumping.
3. The use of biological fermentation is a long and tedious process with reaction time varying between two days and a week, necessitating the use of extremely large storage vats.
4. When acid hydrolysis is used at low pressure, I have found it necessary to run the hydrolysis overnight in order to obtain 50 to 70% of the expected hecogenin yield.
It is obvious to those skilled in the art that such operations as those described above are inefficient and time consuming, and produce very expensive hecogenin, which, from an economic viewpoint alone, limits their use.